Originally Posted by
HillRider
Because the toe clips will drag on the ground and, worse, interfere with cornering when you are using the SPD side of the pedals.
Really? I've seen a few people ride with toe clips that they don't always use, leaving the clips on the lower side of the pedal. They don't drag on the ground and certainly don't interfere with cornering. If you're wanting to do this to a fixie (you didn't say in the OP) and cornering is a problem then if your primary concern is about the looks put something smaller on.
BTW, there are clip-in platforms that fasten to any SPD pedal and allow the use of plain shoes but detach for SPD use. Problem Solvers sells them but you will have to fit your own clips and straps. Winwood sells them both with and without the clips and straps.
That would work.